Harry and Fleur are both suffering after the war.
For Harry, he has seen too much and can no longer comprehend a life without suffering and pain. He jumps at every shadow, his heart is set racing by every little thing. His mind, trained to anticipate danger and never to accept safety, grows more and more tense as the peace stretches on, waiting for a cathartic ambush that will never come.
For Fleur, she has seen just enough. She had never known suffering before the Triwizard tournament, and even in the war she was exposed to very little. For most of the conflict her role was as an informant in Gringotts, and she was not good enough a fighter to serve in any but the most desperate of battles. Battles like the battle for Hogwarts. She saw things there that she couldn't believe, that hearing refused to comprehend. Now, the things she saw haunt her every moment, and prowl like hunters through her dreams.
Everyone around them is recovering and moving on, or else has someone close enough and understanding enough to help them through their coping. They don't. The two of them drift away from their friends, and eventually drift towards each other. They find solace in the silent company of someone just as broken as they are. After some time in this status quo, they learn of one more broken soul. Dennis Creevey.
Dennis Creevey was shattered by the loss of his brother, but with a strength unfathomable to either Harry or Fleur he has carried on. He took up his brother's camera and his passion, sharing the world's wonders with those unable to witness them for themselves. But at night, the young man sits silent and still, surrounded by unmoving pictures, fragments of dead time.
He joins them, but he's different. He's stronger than either of them, but more fragile too, and Harry and Fleur grow to care for him more than even themselves. So, when Dennis says that he is going to climb Mont Blanc the muggle way and capture the beauty of its peak for all wizards to see, Harry and Fleur decide silently that he will not go alone.
Mountains are powerful places. The unmoving witnesses of time and change, they call to the lost like beacons. Three lost souls look up at the summit, only one of whom can see their destination. Harry and Fleur have not yet seen fit to raise their heads, seeing only the very step before them. But as they climb, they will learn. As they climb, they will grow. And as they climb, they might just find each other along the way.
At the foot of the mountain one thing is certain, all three of them dream of the gleaming skies above.